Coating compositions



Patented Feb. 5, 1946 COATING COMPOSITIONS William L. Craig, Westport,Conn assignor to R. T. Vanderbilt Company, Inc., New York, N. Y., acorporation oi New York No Drawing. Application July 25, 1945, SerialNo. 607,104

4 Claims.

This invention relates to fluid coating compositions adapted for thecoating of fibrous sheet materials such as paper. More particularly theinvention relates to fiuid coating compositions of the type generallyknown in the art as coating colors. This application is in part acontinuation of my application Serial No. 422,522, filed December 11,1941, now Patent Number 2,388,526 of November 6, 1945.

Coating compositions of the type known as coating colors usually consistessentially of a mineral or pigment filler such as clay, titaniumdioxide, calcium carbonate, barium sulphate, calcium sulphate, etc.,plus a. prepared adhesive, such as caseinor starch. The finished coatingcomposition may also contain such materials as deroaming agents,leveling agents, etc., and, ii it is to be used to impart color to thefibrous sheet materiaL'the coating composition may also include dyes orcolor pigments. In the preparation oi coating colors of the type mostgenerally used, it has been the practice to disperse the mineral orpigment inwater by mechanical agitation and then mix the resultingcomposition with an adhesive which has previously been preparedseparately. When casein is used as the adhesive, it is first mixedwithwater. An alkaline material such as soda ash, borax, trisodiumphosphate, caustic soda or ammonia is then added and the resultingmixture is then heated. to dissolve the casein. If 2. treated starchsuch as chlorinated gum is to be used as the adhesive, the starch isdispersed in water and heated to put the starch in colloidal solution.When an untreated starch such as raw corn starch, tapioca starch orpotato starch is used, the starch adhesive is usually prepared byadmixing the starch with water and then heating the mixture in thepresence of an amylolytic enzyme to convert the starchinto a mixture ofusable viscosity. In the preparation of coating colors employing starchas th adhesive it has also been proposed to disperse a mixture oi rawstarch and'the mineral or pigment filler in water, and then to heat thisdispersion until the starch is gelatinized after which the resulthisproduct is cooled and the resulting gel is then subjected to extremelyvigorous agitation or grinding in order to mechanically'break down thegel and obtain a product of usable viscosity.

However, all prior coating colors of which I am aware, if they employ astarch adhesive, are characterized by an unusually high viscosity inrelationship to their total content oi starch and filler. Thus priorcoating colors employing starch as the adhesive usually have a viscosityso high as to make their application topaper by brush coating extremelydifficult and sometimes impossible when the total content of starch plusfiller exceeds about 25% Similarly, if the total content of starch and 5filler substantially exceeds 40%, such color coatings, when prepared bythe prior art methods, usually have a viscosity too high to permit theirapplication to paper by any of the conventional machine coating methods.In many instances they are solid and exhibit no flow properties.

The coating colors of my invention employ a starch adhesive preparedfrom raw starch, However, they are characterized by an unusually lowviscosity in relationship to their total content of starch and filler.Thus my novel coating colors hav a viscosity not exceeding about 20,000centipoises as measured by the standard Brookiield Synchro-lectricviscosimeter at 73 F. using a speed of 6 R. P. M., even with a totalcontent of 2a starch plus filler approximating 72%. They are thereforeadapted to be applied to paper by conventional machine coating methods.With total contents of starch plus filler approximating 40%. the coatingcolors of my invention have a viscosity approximating 300 centipoiseswhich is low enough to permit them to be applied readily to paper bybrush coating. With total contents of starch plus filler ranging from aslow as 25% to as high as 72%, the new coating colors of my invention havviscosities that represent only small fractions (approximately 10% orless) of the viscosities of prior coating compositions using starch asthe adhesive and with equivalent total contents of starch plus filler.This extremely low viscosity.

5 in relationship to total content of starch and filler, makes itpossible to apply high coat weights in a single application. Thisgreatly reduces the evaporative burden involved in drying. Moreover,papers coated with the coating colors or my 40 invention have a highergloss than papers coated with generally similar coating colors of theprior art.

In the usual coating colors when using starch as the adhesive, the ratioof starch to filler approximates 1:4 on the weight basis, althoughin'extreme instances this ratio of starch to filler may be as low asabout 15:100, or as high as about 35:100. The governing factor is thatthe proportion of starch used should be sufllcient to bind the mineralor pigment filler to theflbrous sheet with sumcient tenacity to preventpicking during printing. These conventional ratios of starch to fillermay be used satisfactorily in the improved coating compositions of myinvention. The coating colors of my invention are prepared by forming anaqueous suspension a mineral or pigment filler, incorporating a rawstarch in the suspension and then subjecting the resulting mixture tothe action of an amylolytic enzwme. By this procedure, the enzymeconversion of the starch is carried out in the presence of the mineralor pigment filler. The enzyme used in effecting the conversion of thestarch is advantageous- .ly a liquefying enzyme as distinguished from asaccharifying enzyme, particularly a liquefying enzyme produced bybacterial fermentation hav ing a high alpha. amylase content andsubstantially free from beta amylase, insensitive to temperatures up toabout 180 F. and active in alkaline media. The enzymeshould have aliquefon (Analytical edition, Journal of Industrial and EngineeringChemistry, volume '7, pages 143-6, May 15, 1935) content of about500-1200 per gram.

In preparing the new coating compositions of my invention, the desiredproportions of mineral .or pigment and raw starch are thoroughly mixedtogether in water and, when necessary, the pH of the mixture is adjustedto approximately neutral, advantageously within a pH range of from about6.5 to 7.5, by the addition oi'a small amount of either of an alkalinematerial, such as borax, or an acid material, such as alum. A suitableamount of liquefylng enzyme is then added and the mixture is heated toabout 170 F. and held there until the starch is liquefied or until theenzyme converts the starch to the point where the viscosity of themixture is reduced to the desired value. The enzyme is then inactivatedor destroyed. This may be accomplished by raising the temperature to 200F. and holding it there for about minutes. The mixture may then becooled.

My invention will be further illustrated by reference to the followingexamples, but my invention is not limited thereto.

Example I Parts Coating clay 100 Corn starch (raw) 25 Water 53.5 Sodiumsilicate 1.25 Tetrasodium pyrophosphate 0.15 Liquefying enzyme 0.88

The tetrasodium pyrophosphate, used as an agent for dispersing the clay,and the sodium silicate, used to overcomethe tendency of the clay toabsorb protein, were dissolved in water. The dry clay was then added tothe water and dispersed by mechanical agitation. The dry starch and theenzyme were then added to and dispersed in the mixture. The pH (Coleman)of the mixture was then checked and found to be about 7.5. The mixturewas then heated to a temperature of 170 F.-1'75 F. in a cooking tankequipped with a mechanical agitator and held at this temperature for 30minutes while continuing the agitation. The mixture was then heated to200 F.-205 F.

and held for 10 minutes to inactivate the enzyme,

after which the mixture was cooled to room temperature and the viscositymeasured. The viscosity determinations in this instance and in all othertests hereinafter described were made at 73.

F. with a standard Brookfield Synchro-lectric viacosimeter, model L. Vusing a speed of 6 R. P. M.

The coating color produced asjust described had a content of starch andclay of 70% on the total composition, weight basis, and a viscosity of18,600 centipoises. It flowed uniformly and smoothly. A portion of thiscoating color was applied to standard laboratory coating raw stock witha Bird film applicator. The thus coated paper after calendering wastested for coat weight, brightness, gloss, ink receptivity, and abilityto resist "picking" by the Dennison wax test. It was found to have acoat weight of 27.6 (25x38-500), brightness 60.6, loss 50.1, inkreceptivity 5, and to be OK. to #8 wax.

Example I! A coating composition was prepared from the followingmaterials in the proportions indicated, the proportions being given inparts by weight.

Parts Coating clay 100 Corn starch (raw) 25 Water 83.5 Sodium silicate1.25 Tetrasodium pyrophosphate 0.15 Liquefying enzyme 0.63

The procedure employed was the same as that described in Example I. Thecoating color thus prepared had a content of starch and clay of on thetotal composition and a viscosity of 6,000 centipoises.

Example III A coating composition was prepared from the followingmaterials in the proportions indicated, the proportions being given inparts byweight.

The procedure employed was the same as that described in connection withExample I. The coating color thus prepared had a content of starch andclay of 40% on the total composition and a viscosity of 310 centipoises.

Example IV A coating composition was prepared from the followingmaterials in the proportions indicated, the proportions being given inparts by weight.

1 Parts Coating clay 100 Corn starch (raw) 25 Water 3'75 The sameprocedure was used as that described in connection with Example I. Theresulting coating color had a content of starch and clay of 25% on thetotal composition and a viscosity of 10 centipoises.

While coating compositions embodying my invention and in which thecontent of starch and filler varies from about 25% to about 72% on thetotal composition by weight are useful as coating colors, and havesatisfactory pour properties, I prefer such' coating compositions inwhich the content of starch and filler on the total composition variesfrom about 32% to about 65% by weight. Drying of papers coated withcoating colors containing less than about 32% by weight of starch andfiller on the total composition involves an increase in the 'evaporativeburden that is not justified with the coating compositions of myinvention except under unusual circumstances, as where a coated paperwith a very light coat weight is desired for some special purpose. Onthe other hand, in the preparation of coating compositions containingupwards of about 65% of starch and filler on the total composition,initial dispersion of the filler and raw starch is difiicult to obtaindue to the limited amount of water. v

I claim:

i. A fluid coating composition adapted for coating fibrous sheetmaterials consisting essentially of an aqueous suspension oi. particlesof a filler from the group consisting of minerals and pigments and of anamylolyze'd starch produced by the action of an amvlolytic enzyme on rawstarch in an aqueous dispersion of the raw starch and the filler, saidcoating composition containing from about parts to about 35 parts ofstarch by weight for each 100 parts of filler and having a contentoffrom about to about 72% of starch and filler by weight on the totalcomposition, said coating composition having a viscosity not exceedingabout 20,000 centipoises at 73 F.

2. A fluid coating composition adapted for coating fibrous sheetmaterials consisting essentially of an aqueous suspension of particlesof a filler from the group consisting of minerals and pigments and oi anamylolyzed starch produced by the action of an amylolytic enzyme on rawstarch in an aqueous dispersion of the raw starch and the filler, saidcoating composition containing from about 15 parts to about 35 parts ofstarclrby weight for each 100 parts offiller and having a content offrom about 32% to about of starch and filler by weight on the totalcomposition, said coating composition having a "viscosity of less thanabout 20,000 centipoises at 3. A fluid coating composition adapted forcoating fibrous sheet materials consisting essentially of an aqueoussuspension of particles of a filler from the group consisting ofminerals and pigments and of an amylolyzed starch produced by the actionof an amylolytic enzyme on raw starch in an aqueous dispersion of theraw starch and the filler, said coating composition containing fromabout 15 parts to about 35 parts of starch by weight for each 100 partsof filler and having a content of from about 60% to about of starch andfiller by weight on the total composition, said coating compositionhaving a viscosity of less than about 20,000 centipoises at 73 F.

4. A fluid coating composition adapted for coating fibrous sheetmaterials consisting essentially or an aqueous suspension of particlesof a filler from the group consisting of minerals and pigments and of anamylolyzed starch produced by the action of an amylolytic enzyme on rawstarch in an aqueous dispersion of the raw starch and the filler, saidcoating composition containing approximately 25 parts of'starchbyfweight for each parts of fillervand having a content of starch andfiller approximating40%-by weight on the total composition, said coatingcomposition having a viscosity low enough to permit its application tofibrous sheet materials by brush coating.

WILLIAM L. CRAIG.

